After the countdown and the cannonballs, the first group at the first public swim in the Charles River in 50 years had a moment to tread water and look down. It was then that the seven swimmers began shouting their impressions of what the once-famously filthy body of water felt like.

It’s warm, came one report. It feels great, came another. And then a woman looked down and shouted what was unmistakable for the people standing on the dock.

“It’s orange,” a woman shouted as she looked down at her body in the water, which faded to black somewhere around the thighs. “We look orange.”

A man on the dock said it was more like beef broth. Renata von Tscharner, the head of the Charles River Conservancy, said she prefers to describe it as a tea, because she believes that sounds more pleasant.

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Whatever it was, it was clean enough Saturday morning for dozens of people to jump off the River Dock near the Hatch Shell on The Esplanade for the first approved community swim in the Charles River since the 1950s.

Swimming in the Charles River, like playing in the street, is something generations of Boston children have been taught will lead to no good. At the very least, a tetanus shot.

But since 1995, when the EPA gave the water quality a grade of D, the health of the river has improved dramatically, rising to a B in 2011, and now meeting state standards for swimming most days of the summer. The bottom of the river remains a mess of heavy metals and other toxic elements left over from industry, particularly from the period when tidal flow was eliminated by the construction of the Charles River Dam in 1911. But if a swimmer can get in and out of the water without touching the squishy bottom, no tetanus shot is necessary.

Over the past eight years, a group called the Charles River Swim Club — which sounds like something you would read on an ironic T-shirt, the club’s founder concedes — has hosted a 1-mile race for elite swimmers, but Saturday morning was the first time officials allowed a swim for the general public. Getting the permit took six months.

During the course of two hours, about two dozen swimmers at a time took their turn jumping from the dock into the water — which was a comfortable 78 degrees — and playing around for 20 minutes in a small roped-off area while the passing Duck Tour boats beeped their horns. Four lifeguards on the dock, as well as two in kayaks kept watch.

When John Dwinell, the director of aquatics for the state Department of Conservation and Recreation, put on diving gear to inspect the site before the swim and make sure there were no shopping carts or other objects that swimmers might get tangled in — the water near the docks was between 9 and 14 feet deep — he reported visibility was no farther than his hand. But he did find a skateboard, and a fish got “cozy” with him a couple times, he said. The river has famously long carp.

Kathleen McDermott, 56, from Bay Village, said she chose not to think about what might be below her as she swam with the first group of swimmers. “When you’re in the water and you look out and see the view, it’s incredible,” she said.

The public recreational swim was a milestone after decades of work and $500 million in cleanup, and the day was a chance for many of the stakeholders in the river’s issues to celebrate and take a dip.

Bob Zimmerman, the executive director of the Charles River Watershed Association who jumped in with the first group, said it was a big step, but there were many more to come.

“On any given day, you’ve only got a 60 to 70 percent chance that it’s swimmable. A family isn’t going to go through the process of getting down here, packing a cooler, if they might not be able to swim three times out of 10.”

For the day when the Charles has a regular public swimming area, there would also need to be some sort of permanent way to get people in and out of the water without touching the bottom. Several options have been discussed — such as some sort of floating pool in the river — but they are all years and big bucks away from becoming a reality.

When von Tscharner, who had founded the conservancy in 2000 with a swimmable Charles River as one of its goals, jumped in with a later group, she was all smiles as she lay on her back and floated. Karl Haglund, the author of a book called “Inventing the Charles River,” swam up and congratulated her. As she tread water, von Tscharner introduced Haglund as “the man who knows the most about the Charles River,” which prompted a woman nearby to ask Haglund a question.